The present invention relates to water treatment systems, and more particularly, to a circuit for monitoring the status of an ultraviolet bulb in such a system.
Household water treatment systems are gaining popularity--particularly in areas with less than ideal potable water. A household unit is mounted on a single tap to treat selectively water flowing through the tap. Treatment may include filtration, irradiation, or both.
The most effective water treatment systems include ultraviolet (UV) irradiation for sterilizing the water stream. It is well known that such UV treatment kills bacteria and viruses with an extremely high degree of reliability. The water to be treated is routed through a chamber, and a UV light source within or adjacent to the chamber directs UV light through the water stream.
The effectiveness of irradiation depends upon the status of the UV bulb. The bulb may not be operating properly for a variety of reasons. The bulb may be "burned out"; the bulb may be broken; or power to the bulb may be interrupted. Alerting the consumer to a nonoperative bulb is desirable for two reasons. First, the consumer is not getting UV-treated water. Since the water will not look or taste different, the consumer needs to be alerted. Second, if the bulb is broken, glass shards may be in the system. In this case, the bulb also could be trying to light, causing the starter to prematurely fail and/or the ballast to overheat.
A variety of prior art techniques have been developed for monitoring bulb status. A first technique includes positioning a photo detector within the irradiation field to monitor for light emitted from the bulb. However, such detectors are relatively expensive, undesirably increasing the cost of the treatment unit. Examples of this technique can be found in U.S. Pat. Nos. 4,769,131; 4,752,401; 4,682,084; 4,665,627; 4,255,383; 3,948,772; 3,491,234; 3,471,693; 3,182,193; and 2,263,162.
A second technique is to provide an indicator, such as a light-emitting device (LED), that is illuminated when current is flowing through the bulb and unilluminated otherwise. One disadvantage of this technique is that the indicator is illuminated at any time that current is flowing through the circuit regardless of whether the bulb is illuminated. For example, the indicator light would indicate proper operation when the bulb is attempting to light and/or when the circuit is shorted. In neither case is the bulb actually providing irradiation. Consequently, this technique provides a false level of assurance. Examples of this technique are illustrated in U. S. Pat. Nos. 5,023,460; 4,255,663; and 4,141,686. Another illustration of current monitoring, but without an LED, is shown in U.S. Pat. No. 4,615,799.
Bulb intensity control circuits may monitor one or more of lamp output, temperature, voltage, or current, However, the monitored parameters in such systems are used to control bulb intensity only. Such circuits do not provide any indication of the bulb status. Examples of such control systems are illustrated in U.S. Pat. Nos. 4,831,564; 4,471,225; 4,400,270; and 4,336,223.